Characterisation of a household norovirus outbreak occurred in Valencia (Spain)

Abstract

Background: Human noroviruses (NoVs) are the main cause of non-bacterial gastroenteritis worldwide. Several studies have linked human susceptibility to NoVs with the expression of histo-blood group antigens (HBGAs). In January 2012, a NoV gastroenteritis outbreak affected a household in Valencia, Spain, and the personal susceptibility to NoV was investigated.

Methods: To reach this aim 8 members of the affected household were recruited for this study and their secretor status, ABO and Lewis antigens were determined. NoV-specific saliva IgA and serum IgG antibody titers were analyzed. Their capacity to block viral binding to saliva receptors was analyzed, using virus-like particles (VLPs) of the NoV GII.4 genotype, 2006b variant, and saliva from a secretor O blood type donor.

Results: The most relevant finding was that an asymptomatic non-secretor individual shed NoVs in his stools. Interestingly, anti-NoV IgA antibody titers in saliva from secretor and non-secretor individuals showed no differences. On the contrary, high titers of NoV-specific IgG antibody were found in both convalescent sera and in sera collected 1 year post-infection, but only from secretor individuals. NoV GII.4-2006b VLP binding to receptors present in the saliva was efficiently blocked only by sera from secretor positive individuals.

Conclusions: Despite the small number of individuals involved in this outbreak, this study reinforces the idea that susceptibility to human NoV is both dependent on the HBGA profile of the individuals as well as on the viral genotype and variant. We also show that the immunity to NoV lasts for at least 1 year after infection, demonstrating that symptomatic infections strongly stimulate immune responses.

Keywords: Binding assay; FUT2; Histo-blood group antigens; IgA; IgG; Norovirus; Secretor; Susceptibility; Virus-like particles.

Fig. 1

NoV-specific IgA antibody levels. IgA antibody levels against GII.4-Den Haag_2006b NoV VLPs in saliva samples from 6 secretor (left) and 2 non-secretor (right) individuals. The ELISA plates were coated with the NoV VLPs and serial dilutions of saliva samples (1/20 to 1/160) were tested for NoV-specific IgA

Fig. 2

NoV-specific IgG antibody titers and blocking activity of sera from members of a household suffering an acute gastroenteritis outbreak. ELISA plates were coated with NoV VLPs from GII.4-Den Haag_2006b variant to determine the antibody titer according to the secretor (Sese or SeSe) or non-secretor (sese) status. The positive control corresponds to a convalescent serum from another independent gastroenteritis sporadic case. a The upper panel of the figure represents the blocking percentage of the convalescent sera (14 days), from secretors (SeSe and Sese) and non-secretors (sese), that were tested at serial dilutions 1/100, 1/200, 1/400, 1/800 and 1/1,600 (black to clear grey). A percentage higher of 50 % of inhibition was considered as blocking activity. b The lower panel shows the IgG titer against GII.4-Den Haag_2006b VLPs at 2 different times: 14 days (black) and 1 year (grey)